The biochemical processes occurring during antigen-induced stimulation of the precursors of antibody forming cells are poorly understood. The low frequencies of antigen-specific cells within the lymphocyte population have made biochemical studies impractical. It is the aim of the proposed research to circumvent this problem. Hapten-specific murine lymphocytes will be selected by virtue of their ability to bind hapten by their surface immunoglobulin receptors. These cells will be "immortalized" by transformation with temperature-sensitive A gene mutants (tsA) of simian virus 40. Transformed cells, selected on the basis of specific hapten binding, will be cloned and characterized. Since tsA transformed cells tend to lose their transformed phenotypes at non-permissive temperatures, the potential of recovered cell lines to reacquire normal lymphocyte functions under non-permissive conditions will be examined. Characterizations will include: ability to bind hapten specifically, the class(es) of surface immunoglobulin receptors, the ability to respond to lymphocyte mitogens and the ability to respond to hapten-carrier conjugates. Cell lines exhibiting normal lymphocytic patterns of response at non-permissive temperature will be examined for alterations in surface Ig receptors induced by binding of hapten and hapten-carrier conjugates. Of particular emphasis will be attempts to demonstrate a conformational change in the receptors induced by antigen. Parameters to be examined will include changes in the availability of functional groups for chemical modification, alteration in the pattern of receptor susceptibility to proteolytic cleavage, including spontaneous cleavage, and changes in both intermolecular and intramolecular disulfide bonding patterns. The effect of carrier size and the need for accessory cells for any alterations will be examined and correlated with the efficiency of stimulation.